The Preparation And Electrical Properties Of Yttria-stabilized Zirconia

Yttria-stabilized zirconia (YSZ) is widely used as the solid electrolyte in solid oxide fuel cell (SOFC) because of its high oxygen conductivity and good chemical stability under the condition of the application. The density ceramic with good microstructure can be obtained at lower temperature using ultrafine powders with a narrow size distribution, and it may have the good electrical properties.The precipitate containing zirconium and yttrium was prepared using ZrOCl₂ and YCl₃ as raw materials and NH₄HCO₃ as the precipitant. YSZ nanopowder could be obtained by calcining the powder after dealing the precipitate with azeotropic distillation process, and the YSZ ceramics were prepared by sintering the green body obtained after ball milling and uniaxially pressing followed by the isostatically pressing. The precipitate, the powder after azeotropic distillation and the YSZ powder were characterized via TG/DSC,TEM,BET,XRD and some other experiment methods, and the microstructure and electrical property of the ceramic were studied using SEM, EIS and other methods. The results show:1) The molar ratio of Zr and Y in the precipitate is 5.49.2) The azeotropic distillation process can dehydrate effectively, alleviate the aggregation, and reduce the transformation temperature from amorphous zirconia to crystallized zirconia.3) The powders prepared by calcining the precursor after azeotropic distillation process at 800°C for 2 h are less-agglomerated cubic zirconia powders with a narrow size distribution, and the grain size and the specific area of the powders are～20nm and 46.73m²/g, respectively.4) After being sintered at 1350°C for 2 h, the fraction of porosity in the sintered body decreases rapidly, and ceramic obtained at 1350°C has the relative density of 99.3% and the grain size of about 300nm. The relative density of the ceramic sintered at 1500°C for 2h is 99.9%,which reaches up to the maximum.5) The grain boundary conductivity of the ceramic grows up with the rising of the temperature, while the grain conductivity almost has not changes with the altering of temperature. The total conductivities at 1000°C of the ceramics sintered at 1250°C, 1300°C, 1350°C, 1500°C and 1550°C are 0.157 S/cm, 0.173S/cm, 0.191 S/cm, 0.213 S/cm and 0.205S/cm, respectively.6) The activation energies of grain boundary conductivity, grain conductivity and total conductivity change in the rang from 0.7ev to 1.0ev. The relationship between the real grain boundary conductivity (s_gbt) and the apparent grain boundary conductivity (s_gb) can be expressed as s_gbt—0.0075s_gb, which is conducted from the calculated thickness of the grain boundary(2.24nm).